[Remote Store] Update remote store index settings for mixed cluster

[ltaragi]

Is your feature request related to a problem? Please describe

• For MIXED compatibility mode and REMOTE_STORE migration direction:
  • New indices should be remote store backed
  • New indices restored from a snapshot must be remote store backed irrespective of whether the original index was remote store backed or not

Describe the solution you'd like

• This can be accomplished as follows:
  • Look for the MIGRATION_DIRECTION_SETTING and REMOTE_STORE_COMPATIBILITY_MODE_SETTING inside the clusterSettings object
  • Upon finding REMOTE_STORE and MIXED values respectively, obtain the REMOTE_STORE_TRANSLOG_REPOSITORY_NAME and REMOTE_STORE_SEGMENT_REPOSITORY_NAME from any of the remote nodes in the mixed cluster. Information of nodes can be obtained from the clusterState object.
  • Upon finding both repositories, mark the SETTING_REMOTE_STORE_ENABLED as true for the index settings.

Related component

Storage:Remote

Describe alternatives you've considered

No response

Additional context

No response